To read a document using a scanner or the like and store it as image data, it is necessary to accurately detect a document region from a read image. In general, in a flatbed-type or automatic document feeding-type scanner, a document region and another region can be easily discriminated using a backing of a monotone color such as white, black, and the like. However, for example, when a document region color and a backing color are the same, there is a possibility that the document region may not be accurately detected.
Japanese Laid-open Patent Publication No. 2009-272676 discloses an image reading apparatus that determines a document region from a read image, by determining the document region based on a degree of coincidence between apex coordinates of a first rectangle region including all subjects extracted from a read image and apex coordinates of a second rectangle region including all subjects determined as a document content among all the subjects and having a smallest area.
When a document is placed, for example, on a woodgrain desk, it is difficult for an image processing apparatus to accurately discriminate an edge of the document from the pattern of the desk and therefore, in some cases, a region including the pattern of the desk is erroneously detected as a document region.